Method for processing poultry

ABSTRACT

A method for processing poultry, includes supplying live poultry, stunning the live poultry in a stunning device, placing the stunned poultry into product carriers advanced along a conveyor, killing the poultry and removing the feathers from the dead poultry in a plucking device. Downstream of the plucking device, the poultry is exposed to an electrical stimulation, an electrical voltage being applied across the carcass of the poultry. A method for controlling process parameters, especially the time and duration of execution of working steps in a process of mechanized working of slaughtered poultry, includes evaluating the tenderness of a specified meat portion prior to a due processing step and, after this evaluation, setting the important process parameters for the particular processing step to an optimal value.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 10/758,926, filed on Jan. 16, 2004, now U.S. Pat. No. 7,249,998which is a continuation application of PCT/NL02/00480 filed Jul. 17,2002, which is incorporated herein by reference. Priority is claimedfrom The Netherlands Patent Application No. 1,018,566 filed Jul. 17,2001. Each of the above-identified applications is incorporated hereinby reference.

FIELD OF THE INVENTION

This invention relates in general to a method for processing poultry,comprising the steps of supplying live poultry, stunning the livepoultry in a stunning device, placing the stunned poultry into productcarriers advanced along a conveyor, killing the stunned poultry andremoving the feathers from the dead poultry in a plucking device.

DISCUSSION OF THE PRIOR ART

In the poultry-processing industry, poultry such as hens, chickens,turkeys and the like is processed in slaughterhouses, inter alia, intoproducts intended for human consumption. Examples of such edibleproducts are, for example, breast fillets, legs, thighs and productscomprising edible organs, such as, for example, livers and hearts.

Before the poultry can be processed, it is first stunned and thenkilled. The stunning of the poultry is effected, for example, byexposing the poultry briefly to an electric voltage or by placing thepoultry in a room containing a stun gas. The object of stunning thepoultry, either by means of an electric voltage or in some other manner,is to render the poultry semi-conscious, conscious, so that the poultrywill not struggle to free itself from the product carriers. Suchstruggling can result in broken wings and other damage to the poultry,thereby reducing the value of the poultry.

The killing of the poultry is usually effected by cutting the neck, sothat the poultry will bleed to death. It is also possible to re-exposethe poultry to an electric voltage, whereupon the poultry iselectrocuted, however, and therefore killed.

Of great importance to the poultry-processing industry is the supply ofproducts which meet the specific desires of the consumer. In particular,the consumer expects a large measure of quality in the products which hebuys. Within the framework of the present application, the term qualityis defined and hereinafter used as the degree to which a product at acertain moment satisfies the needs, that is to say the expectations anddesires of a specific consumer. One of the quality requirements whichpoultry meat must satisfy is that it should have a sufficient degree oftenderness. Tenderness is a characteristic of meat which is experiencedby the consumer after having prepared the meat in a normal manner.

The degree of tenderness can be measured by conducting so-called sensorymeasurements using a technical or consumer panel. In this, a group ofspecially trained persons is served a number of prepared pieces of meatand is asked to pass judgement on a number of characteristics of themeat, including tenderness. Finally, the persons in the panel rate theproducts on a scale between very tender and very tough. This way ofdetermining tenderness is, however, a subjective method. An objectivemethod for measuring tenderness is the measurement of the so-called“shear force” or shear stress. The shear force can be measured, forexample, with a Warner-Bratzler instrument, in which case ascissors-shaped tool can be used to measure the force which is necessaryto slice through or cut a piece of meat. These measurements can then berecalibrated using a sensory panel.

In addition to the tenderness, the moisture-binding characteristics ofthe poultry meat are also assessed by the sensory panel, both before,during and after the cooking thereof. Together with the visualcharacteristics of the meat (how does it look) and the microbiologicalquality of the meat, the moisture-binding characteristics of the meathave a bearing upon the final tenderness as experienced by the consumer.A high loss of moisture during cooking (high cooking loss) results in adry product, which, though the “shear force” value is the same, isexperienced by the consumer as less tender.

A product having poor tenderness, poor moisture-binding and/or a productwhich has suffered a loss of moisture through spontaneous departure fromthe product (drip loss) or through loss of moisture resulting from thecooking of the product, is experienced by the consumer as a tough andstringy product.

A following quality requirement which the consumer places on the poultrymeat which he finally consumes is that the quality should be as constanta variable as possible. That is to say that a consumer will not accepttoo large a spread in terms of the quality, for example the tenderness,of the product.

From practice, it has already been known for some considerable time thattenderness is a characteristic of meat products which is substantiallydetermined by the time after the death of an animal at which the meat isremoved from the bones. This time is referred to, in practice, as thepost-mortem deboning time and will hereinafter be used as such.

It is an empirical fact that, where post-mortem deboning times areshort, that is to say shortly after the death of a slaughter bird to beprocessed, the outcome is a tough product. At the same time, it is anempirical fact that, in addition to a tough product, a large variationin tenderness also occurs between different products having the sameshort post-mortem deboning time.

The culmination in a tough end product, when deboning is carried out toosoon after death, finds its origin in the following. As long as a muscleremains connected to the skeleton of the poultry, it is not possible forthe muscle to contract unrestricted. A muscle contraction after thedeath of the slaughtered animal is provoked by the so-called “RigorMortis” (RM).

Shortly after the death of an animal, a certain amount of energy isstill present (stored) in its muscles. If a muscle is cut away from theskeleton before RM has set in, then the muscle will severely contractunder the influence of this residual energy still present in the musclein question and the muscle will stiffen. The energy supply still presentin the muscle is substantially present in the form of glycogen, which,via intermediate products such as glucose, is ultimately converted intolactic acid and hence the pH in the muscles will fall. As a result ofthis muscle stiffening, a piece of meat, after having been prepared in anormal manner, will have poor tenderness, which is undesirable with aview to preventing unwanted toughness if the slaughtered poultry is leftto mature for a lengthy period. Such a maturing time, easily, occupies aperiod of about 6 to 24 hours, depending on the kind of poultry. Duringthe maturing period, the poultry is stored and the tenderness of themeat will improve if the meat is deboned once the maturing period hasended.

At the same time, less spread will be found in tenderness between thedifferent birds from the same flock. The late deboning of the producthas, however, a number of drawbacks. Through postponement of thepost-mortem deboning time, together with the tenderness and the spreadtherein, a number of other quality factors change, such as the colour ofthe product, the degree of moisture-binding in the product and thetexture of the surface of the product, the texture of the product, aboveall, having possible repercussions for the further processing of theproduct. Furthermore, as previously stated, when deboning takes place ata late stage after the point of death, the need arises for a maturingperiod in which the slaughter bird has to be stored for a certain time,so that the muscle tissue will tenderize again under the influence ofnatural processes. This is disadvantageous, however, since costlystorage areas have to be provided and there is the risk of the meatbecoming infected whilst the slaughtered birds are stored, the chance ofinfection increasing with increasing storage length.

A possibility for shortening the maturing period and hence arriving at ashorter post-mortem deboning time and the simultaneous improvement ofthe spread in quality of the different products is the use of anelectrical stimulation or electrostimulation of the slaughtered poultryprior to its deboning.

Electrostimulation is a form of direct stimulation of muscle tissue, inwhich the muscle tissue is directly stimulated by applying an electricvoltage across a slaughtered bird. As a result of this stimulation, themuscles are agitated and incited to perform work. As work is performedby the muscles, the glycolysis process in the muscles of the slaughteredbird is accelerated. The glycogen still present in the muscle isultimately converted, via intermediate products such as glucose, intolactic acid. The pH in the muscles thereby falls. Through thestimulation of the muscles, the energy supply is therefore more rapidlyspent, the stimulated muscle enters sooner into RM and the hangingprocess will be accelerated. Deboning can thus be carried out soonerafter death without consequent lack of tenderness having to be sufferedand it is thus possible to debone earlier post-mortem, thereby largelyovercoming the abovementioned drawbacks.

The use of electrostimulation for the tenderization of poultry meat isknown from the American patent publication U.S. Pat. No. 5,888,132.

U.S. Pat. No. 5,888,132 discloses a device and a method for processingpoultry carcasses, especially the electrical stimulation of poultrycarcasses, with the object of tenderizing the meat by exhausting thesupply of stored biochemical energy present in the muscle tissue andproducing an accelerated maturing of the meat. In the known device andmethod, the poultry is suspended from product carriers, the productcarriers being advanced along a conveyor, and the poultry issuccessively stunned, sprayed with water and killed, after which thepoultry is advanced along two electrically conductive rods across whichthere is an electric voltage differential, so that the poultry issubjected to an electrical stimulation. After the electrical stimulationof the carcasses, these are plucked and subjected to further processingoperations, such as deboning and the like.

The electrically conductive rods of the known device are placed in sucha way relative to the carcasses that electrical stimulation takes placeacross the breast portion of the poultry. The carcasses are hereinexposed to a constant electrical stimulation with an alternating voltageranging from 100 to 250 V with a strength of current ranging from 120 to500 mA for a period of 8 to 13 seconds.

U.S. Pat. No. 5,888,132 further teaches an electrical stimulation of thecarcasses by dragging the carcasses through a bath containing a saltsolution, an aqueous solution or by dragging the head of a carcass overa charged metallic mesh or grid, the legs being earthed via the productcarrier.

The use of electrostimulation to accelerate the maturing process is alsoknown from International Patent Application No. 98/19,550.

International Patent Application No. 98/19,550 describes a method foraccelerating the maturing of the carcass of a slaughtered bird, anatural maturing period being avoided. The known method comprises thestep of electrically stimulating the slaughtered bird, the slaughteredbird being exposed to a pulsed voltage for a continuous period.International Patent Application No. 98/19,550 further describes thecooling of the slaughtered poultry after its electrical stimulation. Theslaughtered poultry is cooled to about 5° C., after which it is thentransported to a downstream processing station for the furtherprocessing of the poultry.

International Patent Application No. 98/19,550 further teaches that itis desirable to carry out the electrical stimulation of a slaughteredbird as quickly as possible after the point of death, preferably after90 seconds.

A subsequent use of electrostimulation for accelerating the maturingprocess is known from U.S. Pat. No. 5,512,014.

U.S. Pat. No. 5,512,014 describes a method and a device for electricallystimulating poultry carcasses with a view to tenderizing the meat andshortening the maturing period during processing of the poultry in aslaughterhouse. In the known method, the poultry is subjected toelectrical stimulation some time after the neck has been cut, therebyallowing the poultry to bleed sufficiently dry. The poultry is thenstripped of its feathers and conveyed to a further processing line.

In the abovementioned methods, the electrical stimulation takes place asa step in a processing process for slaughtered birds. Practice hasshown, however, that the yield from the plucking process (pluckability),in which the slaughtered poultry is stripped of its feathers, is damagedby the preceding electrical stimulation. In practice it has been shownthat the stiffening which occurs after electrostimulation in the musclesof slaughtered poultry makes the plucking considerably more difficult asa result of the feathers becoming more firmly entrenched in the skin.Such a reduction in pluckability proves in practice to be a drawback ofthe known method.

It is further a drawback of the known methods that the supply of storedbiochemical energy present in the muscle tissue of the slaughteredpoultry is not fully exhausted during the electrostimulation, so thatfurther considerable stiffening of the muscle tissue will occur. Theneed is still thereby created for a maturing period in which theslaughtered poultry is stored for a certain period to allow the muscletissue to re-tenderize under the influence of natural processes. This isdisadvantageous, however, since costly storage areas have to be providedand there is the risk of the meat becoming infected whilst theslaughtered poultry is stored, the chance of infection increasing withincreasing storage length.

SUMMARY OF THE INVENTION

A first object of the present invention is therefore to provide a methodfor processing slaughtered birds which eliminates the abovementioneddrawbacks.

In accordance with a first aspect of the present invention, a methodaccording to the invention comprises the exposure of the poultry,downstream of the plucking device, to an electrical stimulation for atleast a first stimulation period.

By arranging the electrical stimulation of the poultry downstream of itsplucking, the occurrence of reduced pluckability as a result of theelectrical stimulation is first of all prevented. In addition, thetenderizing effect of the plucking can thereby be utilized. For theplucking of poultry, and especially the mechanical plucking ofslaughtered poultry, has, just like electrostimulation, a tenderizingeffect upon the muscles of the slaughtered poultry. Just as withelectrostimulation, the mechanical plucking sets to work the cells inthe muscles of the poultry and therefore ensures an acceleration of thematuring process and hence the quicker onset of RM. Investigation hasshown that, by carrying out the electrical stimulation of the poultryafter its plucking, the energy supply still present in the muscles canbe further exhausted. This results in a better, that is to say a moretender, end product. The electrical stimulation of slaughtered poultryadditionally has the advantage that, apart from an acceleration of thematuring process, an improvement is additionally attained in the spreadrelating to the characteristics important to the quality of the meatproduct, of which tenderness is one of the more importantcharacteristics.

Moreover, an acceleration of the maturing process in the manneraccording to the invention offers the advantage that deboning can becarried out at an early stage after death (post-mortem), whilstnevertheless maintaining good tenderness of the end product. Inaddition, less storage capacity is required in comparison with the knownmethods and the production processes can take place in-line.Furthermore, a one-day gain is obtained in the shelf life of the endproduct.

In a preferred embodiment of the method according to the invention, anelectric voltage is applied across the carcass of the poultry, or atleast across a part thereof, electrical contact occurring at thelocation of the breast of the carcass, so that a good through-flowthrough the corpse is achieved. In addition, the most meat and the mostimportant portion of meat, which should have the best possibletenderness, is to be found at the location of the breast. In addition,the neck escapes such stimulation, thereby preventing distortion of theneck, which has advantageous consequences for the rest of the process.If, indeed, the neck of the carcass becomes distorted as a result of theelectrical stimulation, the head and neck are made considerably moredifficult to remove.

In a further preferred embodiment of the method according to theinvention, the carcass is led by the breast over at least one electrodeconnected to a power source, preferably an electrically conductive rail,the legs of the carcass being earthed via the product carrier. It isthereby possible to guarantee a substantially constant supply of energyto breast and legs and a good contact is achieved between the carcass tobe stimulated and the electrode.

In a further preferred embodiment of the method according to theinvention, a force is applied to the carcass in the direction of therail as it is led along the rail. In particular, the carcass, at leastwhilst it is being led along the rail, has an oblique positionsubstantially at right angles to its direction of motion. The effect ofthese measures is that the carcass, in the second case under theinfluence of gravity, rests against the rail and remains in slidingcontact with the rail as the carcass is led over it. Furthermore, asecure transfer of energy is realized. In a preferred embodiment of themethod according to the invention, at least a first, zero-voltage restperiod (t₂) is provided after the first stimulation period (t₁) and asecond stimulation period (t₃) after the first rest period (t₂), duringwhich second stimulation period (t₃) the poultry is exposed to anelectrical stimulation in which an electric voltage (V₁) is appliedacross the carcass of the poultry, or at least across a part thereof. Bycarrying out a second electrical stimulation after a first electricalstimulation followed by a zero-voltage period, the (biochemical) energysupply still present in the muscles proved able to be further exhausted.The rigor mortis process which sets in in the muscles of the slaughteredpoultry is thereby substantially accelerated and a more tender productis eventually obtained. The period for further maturing of the poultrycan therefore be shortened.

In a further preferred embodiment of the method according to theinvention, the carcass, during the first stimulation period (t₁) and thesecond stimulation period (t₃), is exposed to a pulsating alternatingvoltage (V₁). The administration of a pulsating current proved to bevery effective. When a pulsating current is used, the carcasses areexposed to a voltage pulse having an associated pulse time and afollowing zero-voltage period having an associated relaxation time.Preferably, the pulse time amounts to about 0.5 second and therelaxation time amounts to about 1 second.

Preferably, during the electrical stimulation of the poultry, a thinfilm of water is applied to the place where the electrical contact takesplace, for example the breast of the poultry, and the electrode is alsomoistened. A very good result is thereby achieved and local(over-)heating of the skin of the poultry and hence possible unwanteddiscoloration is thereby prevented.

A further important criterion in assessing the quality of the meat ofslaughtered animals, especially slaughtered poultry, is the developmentin tenderness. One aspect of the invention is the insight that thegathering of data relating to the tenderness, especially the developmentin tenderness, of the meat at various points in the production processoffers the possibility of finely adjusting this process on the basis ofthe data obtained.

In particular, for a further optimization of the processing process, itis important that the various working steps should be carried out at theright moment (time) and, where applicable, for the most suitableduration.

The object of this is once again to produce a product of the highestpossible quality, in particular as tender a product as possible, withwhich a minimum possible spread in quality-determining factors isadditionally achieved.

In order to achieve this object, the invention according to a secondaspect thereof provides a method for processing poultry whichadditionally comprises the step of controlling process parameters,especially the time and duration of execution of processing steps in aprocess of mechanized working of slaughtered animals, especiallypoultry, consisting in that the tenderness of a specified meat portionis evaluated prior to a due processing step and, after this evaluation,the important process parameters for the particular processing step areset to an optimal value.

If the slaughtered animals are birds, the breast meat is preferablychosen as the meat portion to be evaluated. The evaluation can becarried out prior to the deboning, or prior to the filleting or prior tothe cooling or hanging and, if so desired, prior to the electricalstimulation of the slaughtered bird.

In particular, the evaluation is important for the cooling, since, afterall, the duration of cooling—which precedes the filleting—has a majorinfluence on the quality (tenderness) of the product finally obtained.Lengthy cooling can improve tenderness but demands a lot of energy andthus adds to the cost price; with the proposal of the invention, anoptimal cooling length can be set and corresponding savings can berealized.

Furthermore, the evaluation of tenderness prior to the electricalstimulation is advantageous. As already described above, the electricalstimulation of slaughtered poultry has a positive influence on thetenderness and development in tenderness of the poultry. This influencecan be still further enhanced if, prior to the electrical stimulation,the (instantaneous) tenderness of the poultry is known and, on the basisof these data, the electrostimulation process can then be controlled insuch a way that an optimal effect can be achieved.

Therefore the combination of measuring the tenderness during theprocessing process, controlling the various working steps on the basisthereof and, in particular, electrically stimulating the slaughteredbirds is an especially suitable way of producing a very tender productover a very short maturing period, a very low spread additionally beingobtained in the characteristics important to the quality of the product.

The tenderness can be determined by measuring the respective diffusereflection coefficients of this specimen for radiation with differentspecified wavelengths in the visible and near-infrared zone, bycomparing the measurement values thus obtained with those obtained froma similar determination carried out on specimens having a knowntenderness measure and by deriving therefrom a variable whichcharacterizes the tenderness in question.

In this context, for example, two reflection coefficient determinationscan be carried out for radiation wavelengths in the visible lightspectrum, combined with two in the near-infrared spectrum.

Tenderness-related information would also be obtained by subjecting themeat part to a concentrated blast, of predetermined duration andintensity, of a flowing medium, whilst closely observing the evolutionof the resultant surface deformation in the meat. Air can be used as theworking medium.

A preferred embodiment of the invention is that with which a definitivemeasurement variable, representing tenderness, is obtained by combininga number of determinations carried out at different radiationwavelengths.

Preferably, the mode of procedure in this case is that measurementvariables are regularly determined of new meat specimens of knowntenderness and a databank is thus created in which the correlation isestablished between the results of the determinations and the tendernessexperienced in practice.

A concrete device for implementing the proposed method can be realizedwith a nozzle for the targeted and controlled discharge of a blast ofcurrent of a medium, a detection device, interacting therewith, fordelivering an electrical output signal representing the behaviourpattern of the impression formed in the meat to be evaluated, and aprocessing circuit for sampling characterizing parts of the detectionsignal obtained. The processing circuit is here set up to analyze theinitial formation, the maximum size and the relaxation of signal partsrepresenting the impression to be evaluated.

A system for evaluating the tenderness of a meat part of a slaughteredanimal, especially slaughtered poultry, utilizing the above-describedmethods comprises means for comparing the respective measurement resultsobtained from a conducted evaluation with those obtained during a seriesof previously conducted determinations and for, on the basis thereof,delivering a measurement value representing the tenderness. Thismeasurement value can then be used to control the product process.

The preceding and other aspects, characteristics and advantages of thepresent invention will be illustrated in greater detail below withreference to the drawings and with reference to the followingdescription of examples of a method according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic outline drawing of a poultry-processing plant,having indicated thereon the places where the method according to theinvention can advantageously be used;

FIG. 2 is a block diagram representation of a device for implementingthe proposed method;

FIG. 3 reproduces a graph indicating the behaviour pattern of thesurface deformation formed during the implementation of the method;

FIG. 4 is a diagrammatic representation of a first embodiment of adevice according to the invention;

FIGS. 5 a and 5 b are diagrammatic representations of a secondembodiment of the invention;

FIG. 6 shows diagrammatically a third embodiment of the invention, and

FIG. 7 illustrates a fourth embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the processing operation in a slaughterhouse to form poultry partsfit for human consumption, the following steps are realized in general.First of all, the still live poultry is fed, for example in crates, to astunning device. In the stunning device the poultry is brought into asemi-conscious or unconscious state, allowing the poultry to be hung byits legs in product carriers which are known per se and are advancedalong a conveyor. The poultry can be stunned by the use of a controlledgas environment, in which the birds lose consciousness, inter alia dueto oxygen deficiency, or by the administration of an electric shock.Usually at the moment when the poultry is just regaining consciousness,the neck of the poultry is cut, so that the bird is killed and willbleed dry. The poultry is next stripped of its feathers in a pluckingdevice provided for this purpose and the poultry can further beprocessed in downstream processing stations, such as eviscerationdevices for the harvesting of organs, dividing devices for cutting thecarcass of the poultry into parts and deboning devices for cutting awaythe meat from the bones of the carcass. In the deboning of the carcass,consideration must however be given to the following. Shortly after thedeath of an animal, an energy supply is still present in the muscles.This energy supply is slowly used up, the so-called maturing or hangingof the meat. This maturing period, easily, occupies a period of 6 to 24hours. During the maturing, a stiffening and hence a shortening of themuscles, rigor mortis, occurs. If a muscle is cut away from the skeletonbefore rigor mortis has set in, the muscle will severely contract,without this being prevented by a connection to the bones, and themuscle will stiffen.

The result of this is that a stiffened muscle, after having beenprepared by a consumer in a normal way, will be experienced by thisconsumer as a very tough meat product. If a bird is therefore debonedshortly after the point of death, then a tough product is obtained. Atthe same time, it is an empirical fact that, in addition to a toughproduct, a large variation in tenderness also occurs between differentproducts having the same short post-mortem deboning time.

One possibility of shortening the maturing period and hence arriving ata shorter post-mortem deboning time is to use an electrical stimulationof the slaughtered poultry prior to its deboning.

The present invention is based on the insight that the effect of anelectrical stimulation of slaughtered poultry for shortening thematuring period in order thereby to achieve shorter deboning times isfavourably influenced if poultry is plucked prior to its electricalstimulation. By having the electrical stimulation of the poultry takeplace downstream of its plucking, reduced pluckability arising from theelectrical stimulation is prevented. In addition, the tenderizing effectof the plucking is utilized. The plucking of poultry and, in particular,the mechanical plucking of slaughtered poultry has a tenderizing effectupon the muscles of the slaughtered poultry by virtue of the cells inthe muscles of the poultry being set to work.

Research has revealed that, by carrying out the electrical stimulationof the poultry after its plucking, the energy supply still present inthe muscles can be further exhausted, thereby resulting in a more tenderend product.

The administration of an electrical stimulation according to a firstpreferred embodiment of a method according to the invention is carriedout as follows.

The poultry suspended in product carriers, which product carriers areadvanced along a conveyor, is moved forward and, as it is transported,is dragged by the head through a bath containing a salt solution or anaqueous solution. The legs of the carcass are earthed via the productcarrier, so that the poultry is subjected to an electrical stimulation(whole body flow). Another possibility is that the carcasses areadvanced along two electrically conductive rods, the electricallyconductive rods being placed in such a way relative to the carcassesthat electrical stimulation takes place across the breast portion of thecarcass.

Another very favourable possibility is a combination of thepossibilities just stated, namely the earthing of the legs of thecarcass via the product carrier and the advancement of the carcass, bythe breast, over an electrically conductive rail connected to a voltagesource or over a strip-shaped electrode. In order to guarantee thecontact between the breast of the carcass and the rail (or strip-shapedelectrode), a force is applied to the carcass in the direction of therail as it is led along the rail. In particular, the carcass, at leastwhilst it is led along the rail, has an oblique position substantiallyat right angles to its direction of motion, which can be achieved, forexample, by placing the rail in such a way relative to the track, of theproduct carriers that the carcass, under the influence of gravity, willrest against the rail as it travels over it. The carcass consequentlyremains in sliding contact with the rail, a very good flow through thebody is achieved and the electrical stimulation can be carried out veryeffectively.

Another option is to direct an air current onto the carcass as it is ledover the rail or, for example, to use a second (non-conductive) rail onthe rear side of the carcass, so that the carcass is clamped between therails as it is led over the electrically conductive rail.

During the electrical stimulation of the poultry, it is advantageous toapply a thin film of water to the place where the electrical contacttakes place, for example the breast of the poultry. If the electrode isalso moistened, a very good result is achieved and local (over-)heatingof the skin of the poultry and hence possible unwanted discoloration isprevented.

The carcasses are hereupon exposed to an electrical stimulation with apulsating alternating voltage V₁ of 100 V and a frequency F₁ of 50 Hzfor a first stimulation period t₁ of about 90 seconds.

Research has revealed that the administration of a continuous current isless effective than a pulsating current. When a pulsating current isused, the carcasses are exposed to a voltage pulse having an associatedpulse time and a following zero-voltage period having an associatedrelaxation time. Preferably, the pulse time amounts to about 0.5 secondand the relaxation time amounts to about 1 second.

In a second preferred embodiment of a method according to the invention,in which slaughtered poultry is exposed to an electrical stimulationsubstantially in the same way as in the first preferred embodiment,after the electrical stimulation over the first stimulation period t₁ arest period t₂ is provided, during which rest period the poultry is notexposed to an electrical voltage, and after the rest period t₂ a secondstimulation period t₃ is provided, during which stimulation period thepoultry is exposed to an electrical stimulation which is whollyconsistent with the electrical stimulation over the first stimulationperiod t₁. In this way, as research has shown, the (biochemical) energysupply still present in the muscles can be further exhausted. The rigormortis process is thereby substantially accelerated.

To a person skilled in the art it will be clear that the embodimentsdiscussed are not limited to the stated durations. According to thecircumstances, it is quite conceivable for the stimulation periods t₁and t₂ to be longer or shorter, for example 2.5 minutes or 4.5 minutes.Furthermore, the rest periods can also be longer or shorter. It isadditionally conceivable that, after the second stimulation period t₂, asecond rest period t₄ followed by a third stimulation period t₅ is used,with a view to exhausting the energy supply in the muscles stillfurther.

As previously discussed, the use of an electrical stimulation onslaughtered poultry has an accelerating effect upon the maturing of themeat. It is thereby possible to cut the meat away from the bone to whichit is attached sooner after the point of death, in which case the finalquality of the end product continues to be guaranteed. In particular, itis possible to debone downstream of the electrical stimulation after amaturing period of about two to three hours post-mortem.

During the process for processing poultry in a slaughterhouse, a choicehas to be made on when the maturing process has progressed far enoughfor the said quality of the end product to be able to be guaranteed. Afirst option is to choose a fixed point within the said maturing periodand to proceed with further processing of the poultry after thismaturing period. It is also possible, however, to decide on the point atwhich further processing can proceed on the basis of changing parametersof the meat during the maturing period and hence during transport of thepoultry (in-line).

A first possible parameter on which such a decision can be based is theacidity or pH of the meat. As previously discussed, during the maturingprocess of the meat the energy supply still present in the muscle isused up. This energy supply is used by the muscle to contract(contraction) and to relax (relaxation), for which the muscle requirescalcium and adenosine triphosphate (ATP). Muscle contraction takes placeat the moment at which, as a result of a signal from the nervous system,a large quantity of calcium is released into the muscle fibre, whichleads to large numbers of contractions, thereby depleting the ATPquantity. For a cell, it is easily still possible to synthesize new ATPthrough an anaerobic process, glycolysis. The glycogen in the muscles isultimately converted, via intermediate products such as glucose, intolactic acid, as a result of which the pH in the muscles will fall duringthe maturing process. By measuring the pH just after the completion ofthe electrical stimulation or some time afterwards, a prediction can bemade on the basis of known data concerning the suitable point at which astart can be made on the further processing.

A second option is to measure in the muscle the degree of exhaustion ofthe quantity of energy store present, in order to base a decision onthis.

In the initial post-mortem period, a muscle tries to maintain a balancedequilibrium between adenine nucleotides; the ATP level remains constantor declines somewhat. If the glycogen store diminishes, the formation ofATP through glycolysis also diminishes. The ATP is dephosphorylated intoadenosine diphosphate (ADP) and adenosine monophosphate (AMP). From twoADP molecules, 1 ATP and 1 AMP molecule are formed. In order to allowthis reaction to proceed, the AMP is virtually directly deaminated intoinosine monophosphate (IMP). IMP can no longer be converted back intoATP. Finally the IMP is systematically converted into inosine andultimately into hypoxanthine. A parameter for measuring the progress ofthis process is the so-called R-value, which is an important parameterfor the progress of rigor mortis. The R-value is the ratio of theadenine nucleotides (ATP, ADP and AMP) and their breakdown products(IMP, inosine and hypoxanthine). The choice of a certain value of theR-value, at which the meat will have acceptable tenderness, can help todecide the point at which the poultry can be further processed.

The method of electrically stimulating slaughtered poultry after thepoultry has been plucked has been discussed at length above. Practicehas shown that, in methods known in the prior art, an electricalstimulation has a negative effect upon the pluckability of the poultryif the electrical stimulation precedes the plucking.

As a solution for preventing this adverse effect of electricalstimulation, in addition to having the execution thereof take placeafter the poultry has been plucked, a short electrical stimulation canalso be carried out immediately prior to the plucking. The subcutaneousmuscles consequently have virtually no opportunity to stiffen and thepluckability of the poultry is scarcely impaired. A period of about 50seconds post-mortem should be contemplated in this respect.

As already described above, a further important criterion when assessingthe quality of the meat of slaughtered animals, especially slaughteredpoultry, is the development in tenderness. An insight into this can beacquired by the gathering of data relating to the tenderness, especiallythe development in tenderness, of the meat at various points in theproduction process, thereby offering the possibility of finely adjustingthis process on the basis of the data obtained.

A further option of deciding on the point at which further processingcan proceed on the basis of changing parameters of the meat over thematuring period, and hence during transport of the poultry (in-line), isdescribed below with reference to FIGS. 1 to 7.

A modern poultry-processing plant according to the prior art, in FIG. 1denoted in its entirety by reference numeral 100, comprises a deliveryand unpacking station 102, the so-called slaughter line 104, pluckingline 106, dressing line 108, cooling line 110 and, finally, a deboningand filleting line 112, where the meat of the slaughtered poultry isseparated from the bones. Each of these “lines” contains a combinationof working stations, all of which is known per se and is consequentlynot explained in any further detail.

A first place where it can be interesting to obtain data relating to thetenderness of the meat of the poultry to be processed is the position A,i.e. directly before the plucking. There a first quantity of data isthen obtained, relating to the quality of the supplied poultry.

A second position of interest is the position B, directly after the“dressing” operation, i.e. after a carcass has been split into parts buthas not yet been deboned or filleted. In the position C, too, precedingthe cooling, an evaluation of the tenderness of the meat can provideinteresting data on the basis of which the further process can be finelyadjusted. A determination at the position D—i.e. during the cooling—andposition E—after the cooling—enables supplementary data to be obtained,which is also true of the evaluation in the positions F, G and H, i.e.in the deboning and filleting line, whether or not the bleeding timesand/or instants, the heating times and/or instants, and/or the pluckingtimes and/or instants are adjustable or in need of adjustment.

By far the most interesting is the evaluation in the position C, sincehere the tenderness of the meat is evaluated before the carcass isdissected into parts (deboning, filleting) and the data herein obtainedcan more widely influence the following process duration, especially theduration of the cooling and any intermediate storage prior to filletingand deboning. If the evaluation reveals, for example, that no lengthycooling or intermediate storage is necessary to obtain satisfactorytenderness in the end product, the process duration can be regulatedaccordingly, whereby substantial savings can be made.

A device with which the evaluation can be realized is shown indiagrammatic representation in FIGS. 2 and 3. A meat part to beevaluated is denoted by 120; the housing 121 of the device which actsthereupon comprises a spray nozzle 122, which, via an electric valve 126to be regulated from a control circuit 124, is connected to a pressuresource 128 of the medium used, for example air. Another suitable medium,possibly a liquid, can also be used. The impression 132 formed by theaction of the discharged jet 130 in the surface 120 a of the meat part120 is “viewed” by a suitable detector 134, also accommodated in thehousing 121. This detector 134 can comprise, for example, aradiation-sensitive detector 138, which interacts with converters 136transmitting flashes of light which are reflected by the bottom of the“impression” 132 and, after reflection, fall upon the detector 138; therunning time elapsed between the transmission of a pulse by theconverters 136 and the return received after the reflection and by thedetector 138 is then a measure of the “depth” d of the impression 132,since the distance between detection device and surface 120 a is, afterall, known. It is also conceivable to use a system which operates in themanner known from the modern cameras and which can determine thedistance between an image plane and an object plane.

In whatever way: the device 134 delivers, at its output 140, an electricvoltage, the behaviour pattern of which represents the evolution of theformed impression 132. This voltage is supplied to suitable processingcircuits 142, 144 (possibly analog/digital converters, interfacecircuits, memory stores, etc.), the realization of which is not asubject of the invention. It is conceivable to store the evaluationresults of a number of standard test pieces as standard in a memory inthe circuit 144 and to produce an evaluation result using an effectivecomparator. The circuit 144 has three outputs: the one, 144 a, feeds theevaluation result in suitable form to the printer 146; and the second,144 b, feeds the evaluation result in suitable form to the display 148and the third, 144 c, feeds the evaluation result in the form of aparameter variable to a central control unit (not specifically drawn),by which the throughput times in the various working lines of the plantare set.

It should be noted that, in fact, the printer 146 and the display 148can suffice: in this case an operator can directly read off theevaluation result and, on the basis thereof, finely adjust the process.

FIG. 3 shows the graphic representation of the behaviour pattern of theoutput voltage of the detector 138 representing the depth d, namely inthe form of the path of the curve 150. At the moment T1, the “radiationpulse” starts and the depth d of the formed impression begins toincrease to the value d_(max) at the moment T2. After this the depthremains more or less constant to the moment T3, the moment at which the“radiation pulse” ends. The depth then declines again to a residualvalue, denoted by d_(res).

For the evaluation of the tenderness, the path of the curve between thepoints a and b thereof, i.e. between the times T1 and T2, and, in fact,the value of the angle α are of interest. This can be simply determinedby differentiating the output voltage of the detector between themoments T1 and T2. Also of interest is the maximum depth of impression,which follows from the maximum value of the output voltage. If, at themoment T3, i.e. at the moment c of the curve 150, the radiation pulsestops, the meat starts to recover and the depth of impression d declinesagain to a residual value d_(res), which is reached after the moment T4,at the point d of the curve. Here, too, the value of the angle β isagain of interest, which value can be simply determined. The assessmentof the curve 150 does not therefore call for any very highly developedelectronics.

By determining in advance, for a large number of meat pieces of knowntenderness, the curve represented in FIG. 3, with its associatedvariables, and storing this all in a memory, a comparison of themeasurement result with these “calibration data” enables a pronouncementto be made, with a good degree of certainty, about the tenderness of themeat.

FIGS. 4 to 6 show diagrammatically some illustrative embodimentsaccording to the invention by which a determination is carried out onthe meat of a slaughtered animal which is still suspended from aconveyor track. FIG. 4 shows a transport hook 155 which is led along atrack 154 and from which an already plucked carcass 156 is hanging,which carcass, at the place of the measuring arrangement, bears againstthe stop rod 158. The device contains the aforementioned nozzle 160,connected via the controlled valve 162 to a pressure source,symbolically indicated by the arrow 164; the detection portion locatednear the nozzle 160 is not visible in this figure but can be realized inthe manner explained with reference to FIG. 2. The measurement resultobtained is represented on the monitor 166 connected to the evaluationand processing electronics 168. Within the circle 170 there isrepresented, on an enlarged scale, the impression 172 formed in themeat, as previously discussed.

FIG. 5 a relates to the case in which the carcass 180, with its legs 182suspended from the customary suspension hook 184, has not yet beenplucked, so that the disruptive influence of the feathers present needsto be overcome. To this end, use is made according to this figure of asort of “shaving” bar 186 having rotating knives 188, which arerepresented on an enlarged scale at 189. The whole is supported by asuitable holder 190, in which the various drive units are alsoaccommodated.

FIG. 5 b shows how, after this “clean-shaving”, the evaluation isconducted in the manner explained with reference to FIG. 4: theapparatus used is in both cases the same.

FIG. 6 shows an embodiment which broadly coincides with that accordingto FIG. 4 but which has been made suitable for carrying out anevaluation on poultry yet to be plucked. To this end, there is a secondnozzle 200; through this nozzle, a gentle air jet is aimed at the spot202 to be evaluated on the breast side of the poultry, so that thefeathers 204 present there are blown apart and the evaluation can becarried out using the device conforming to that according to FIG. 4.

FIG. 7, finally, shows how the device can be simply deployed to assesspieces of meat of slaughtered birds, for example breast fillets 300a-300 d, which are guided by means of the conveyor track 302 along theevaluation device 304. Here too, the evaluation device comprises thespray nozzle 306 and still visible behind it in this figure there is aportion of the detection device 308, realized in accordance with thedetection device explained with reference to FIG. 2.

To a person skilled in the art, it will be clear that the scope of thepresent invention is not limited to the embodiments described above butthat various changes and modifications can be made thereto withoutdeviating from the scope of the invention as defined in the attachedclaims.

It is thus possible, for example, to apply the gathering of datarelating to the tenderness of the slaughtered birds independently fromthe electrical stimulation of the slaughtered birds, it is also possibleto apply the electrical stimulation of the slaughtered birdsindependently from the gathering of the said data.

1. A method for processing poultry, comprising the steps of: supplying live poultry; stunning the live poultry in a stunning device; placing the stunned poultry into product carriers advanced along a conveyor; killing the stunned poultry; removing the feathers from the dead poultry in a plucking device; and exposing the poultry to an electrical stimulation upstream and downstream of the plucking device.
 2. The method according to claim 1, wherein the electrical stimulation upstream of the plucking device is carried out at a period prior to the plucking so that the poultry is not stiffened when plucked.
 3. The method according to claim 1, wherein the electrical stimulation upstream of the plucking device is carried out immediately prior to the plucking.
 4. The method according to any one of claims 1-3, wherein the electrical stimulation upstream of the plucking device is carried out within a period of about 50 seconds post-mortem.
 5. The method according to claim 1, wherein the electrical stimulation downstream of the plucking device is carried out for at least a first stimulation period.
 6. The method according to claim 5, further comprising the step of deboning the poultry after at least the first stimulation period following the expiry of a waiting period.
 7. The method according to claim 6, further comprising the step of cooling the poultry, after at least the first stimulation period, during the waiting period.
 8. The method according to claim 1, wherein an electric voltage is applied across the carcass of the poultry, or at least across a part thereof, by the carcass being dragged by the head through a bath connected to a power source and containing an aqueous solution, the legs of the carcass being earthed via the product carrier.
 9. The method according to claim 1, wherein an electric voltage is applied across the carcass of the poultry, or at least across a part thereof, electrical contact occurring at the location of the breast of the carcass.
 10. The method according to claim 9, wherein the carcass is led by the breast over an electrode connected to a power source.
 11. The method according to claim 9, wherein the carcass is led by the breast over an electrically conductive rail connected to a power source.
 12. The method according to claim 11, wherein a force is applied to the carcass in the direction of the rail.
 13. The method according to claim 9, wherein the legs of the carcass are earthed via the product carrier.
 14. The method according to claim 9, wherein a thin film of water is provided at the place where the electric voltage is applied.
 15. The method according to claim 1, further comprising the step of controlling process parameters in a process of mechanized working of slaughtered poultry, wherein the tenderness of a specified meat portion is evaluated prior to a due processing step and, after this evaluation, the important process parameters for the particular processing step are set to an optimal value.
 16. A poultry-processing plant for processing poultry, comprising: a supply station for supplying live poultry; a stunning device for stunning the live poultry; a station for placing the stunned poultry into product carriers of a conveyor; a killing device that kills the stunned poultry; a plucking device for removing the feathers from the dead poultry; and an electrical stimulation device for exposing the poultry upstream and downstream of the plucking device to an electrical stimulation.
 17. The poultry-processing plant according to claim 16, wherein the electrical stimulation device is configured to apply an electric voltage across the carcass of the poultry, or at least across a part thereof, such that electrical contact occurs at the location of the breast of the bird.
 18. The poultry-processing plant according to claim 17, wherein the electrical stimulation device comprises—an electrically conductive rail connected to a power source, the rail being configured such that a carcass is led over the rail by the breast.
 19. The poultry-processing plant according to claim 16, wherein the electrical stimulation device comprises an electrode connected to a power source, the electrode being configured such that the carcass is led over the electrode by the breast.
 20. A poultry-processing plant for processing poultry, comprising: a supply station for supplying live poultry; a stunning device for stunning the live poultry; a station for placing the stunned poultry into product carriers of a conveyor; a killing device that kills the stunned poultry; and a plucking device for removing the feathers from the dead poultry; and an electrical stimulation device for exposing the poultry downstream of the plucking device to an electrical stimulation for at least a first stimulation period.
 21. The poultry-processing plant according to claim 20, wherein the electrical stimulation device is configured to apply an electric voltage across the carcass of the poultry, or at least across a part thereof, such that electrical contact occurs at the location of the breast of the bird.
 22. The poultry-processing plant according to claim 21, wherein the electrical stimulation device comprises an electrically conductive rail connected to a power source, the rail being configured such that a carcass is led over the rail by the breast.
 23. The poultry-processing plant according to claim 20, wherein the electrical stimulation device comprises an electrode connected to a power source, the electrode being configured such that the carcass is led over the electrode by the breast.
 24. A poultry-processing plant for processing poultry, comprising: a supply station for supplying live poultry; a stunning device for stunning the live poultry; a station for placing stunned poultry into product carriers of a conveyor; a killing device that kills the stunned poultry; a plucking device for removing feathers from dead poultry; and an electrical stimulation device for exposing poultry downstream of the plucking device to electrical stimulation. 